So that's why this story this week made me so happy. :)
One Small Step for Fish ...
Times Staff Writer
April 6, 2006
U.S. researchers have found fossils of what they say is a missing evolutionary link between fish and land animals — a strange creature that first crawled onto the shore about 375 million years ago.
The fossils, found on Ellesmere Island in Arctic Canada, suggest the limbs, skull, neck and ribs of four-limbed animals, but also the primitive jaw, fin and scales of fish, scientists reported today in the journal Nature.
"This really is what our ancestors looked like when they began to leave the water," said an accompanying editorial by zoologist Jennifer A. Clack of the University of Cambridge and biologist Per Erik Ahlberg of Uppsala University in Sweden.
The newly discovered species, called Tiktaalik roseae, "blurs the boundary between fish and land-living animal both in terms of its anatomy and its way of life," said biologist Neil Shubin of the University of Chicago, a co-leader of the expedition.
The creature lived in shallow waterways, where it hunted for prey with its crocodile-like snout and sharp teeth, but was able to pull itself out of the water for short periods of time and move around on its limb-like fins, scientists said.
The specimens, ranging from 4 to 9 feet long, were remarkably well-preserved. The scientists were able to examine the joints and to conclude that the shoulder, elbow and wrist joints were strong enough to support the creature's body on land.
"Human comprehension of the history of life on Earth is taking a major leap forward," said H. Richard Lane of the National Science Foundation, which funded the research along with the National Geographic Society and other groups.
"These exciting discoveries are providing fossil Rosetta Stones for a deeper understanding of this evolutionary milestone — fish to land-roving tetrapods," he said.
In the late Devonian period, nearly 400 million years ago, the landmass where the fossils were found straddled the equator and had a climate much like that now found in the Amazonian basin. It was a flat coastal plain with shallow, slow-moving rivers that meandered to the sea.
"This kind of shallow stream system seems to be the place where many features of land-living animals first arose," said expedition co-leader Ted Daeschler of the Academy of Natural Sciences in Philadelphia.
But as Earth's continental plates shifted, the mass was carried north to Canada's Nunavut territory in the Arctic Ocean.
Finding and extracting the fossils presented major challenges, such as the need to travel by helicopter into the region.
Freezing temperatures and high winds limited the amount of time the team could work each day, and the near-constant precipitation prevented the plaster used in the fossil-preservation process from drying. "And we were always looking over our shoulders for polar bears. We saw lots of their tracks," Shubin said. Team members all carried guns for protection.
The key breakthrough came on a 2004 fossil hunting expedition — one of five yearly trips — when team members spied the front end of what looked like a fish skull sticking out of the bluff. "That's ideal — having the snout sticking out — because in the cliff behind it is likely the rest of the animal," Shubin said.
The researchers ultimately found three nearly complete specimens, but they weren't sure what they had until they returned to the lab and studied the bones.
"As each piece to Tiktaalik's anatomy was exposed, we began to see just how wonderfully intermediate this animal's features were between land and water," Shubin said.
The creature had a flat skull, like that of a crocodile, but it had armor like a fish, scientists said. And it had a neck, they said, making it the only fish known to have one. "The neck was one of the biggest surprises," Daeschler said. "This freed the skull from the shoulder girdle and gave the animal extra mobility."
At the ends of the powerful fins, the team found wrists and bones similar to fingers. But the fins also contained the thin rods found in fish fins. "Here is a creature with fins that can do push-ups," Shubin said.
And instead of the tiny rod-like ribs of a fish, Tiktaalik had full-fledged ribs that overlapped one another like those of an anteater. "Ribs like that produce a stiff trunk," said Farish A. Jenkins of Harvard University, another expedition leader.
"Fish that stay in the water are buoyant and don't need that, so this animal must have developed these structures for life in the shallows and making excursions onto land," he said.
Shubin said: "This animal is both fish and tetrapod. We jokingly call it a 'fishapod.' "
Rather than following the convention of using Latin for a species' name, the research team asked the Nunavut elders council for suggestions. It recommended Tiktaalik, which means "a large shallow-water fish" in the Inuktitut language. Roseae honors an anonymous donor.
Fossil Called Missing Link From Sea to Land Animals
Scientists have discovered fossils of a 375-million-year-old fish, a large scaly creature not seen before, that they say is a long-sought missing link in the evolution of some fishes from water to a life walking on four limbs on land.
In two reports today in the journal Nature, a team of scientists led by Neil H. Shubin of the University of Chicago say they have uncovered several well-preserved skeletons of the fossil fish in sediments of former streambeds in the Canadian Arctic, 600 miles from the North Pole.
The skeletons have the fins, scales and other attributes of a giant fish, four to nine feet long. But on closer examination, the scientists found telling anatomical traits of a transitional creature, a fish that is still a fish but has changes that anticipate the emergence of land animals — and is thus a predecessor of amphibians, reptiles and dinosaurs, mammals and eventually humans.
In the fishes' forward fins, the scientists found evidence of limbs in the making. There are the beginnings of digits, proto-wrists, elbows and shoulders. The fish also had a flat skull resembling a crocodile's, a neck, ribs and other parts that were similar to four-legged land animals known as tetrapods.
Other scientists said that in addition to confirming elements of a major transition in evolution, the fossils were a powerful rebuttal to religious creationists, who have long argued that the absence of such transitional creatures are a serious weakness in Darwin's theory.
The discovery team called the fossils the most compelling examples yet of an animal that was at the cusp of the fish-tetrapod transition. The fish has been named Tiktaalik roseae, at the suggestion of elders of Canada's Nunavut Territory. Tiktaalik (pronounced tic-TAH-lick) means "large shallow water fish."
"The origin of limbs," Dr. Shubin's team wrote, "probably involved the elaboration and proliferation of features already present in the fins of fish such as Tiktaalik."
In an interview, Dr. Shubin, an evolutionary biologist, let himself go. "It's a really amazing, remarkable intermediate fossil," he said. "It's like, holy cow."
Two other paleontologists, commenting on the find in a separate article in the journal, said that a few other transitional fish had been previously discovered from approximately the same Late Devonian time period, 385 million to 359 million years ago. But Tiktaalik is so clearly an intermediate "link between fishes and land vertebrates," they said, that it "might in time become as much an evolutionary icon as the proto-bird Archaeopteryx," which bridged the gap between reptiles (probably dinosaurs) and today's birds.
The writers, Erik Ahlberg of Uppsala University in Sweden and Jennifer A. Clack of the University of Cambridge in England, are often viewed as rivals to Dr. Shubin's team in the search for intermediate species in the evolution from fish to the first animals to colonize land.
H. Richard Lane, director of paleobiology at the National Science Foundation, said in a statement, "These exciting discoveries are providing fossil 'Rosetta Stones' for a deeper understanding of this evolutionary milestone — fish to land-roaming tetrapods."
The science foundation and the National Geographic Society were among the financial supporters of the research. Besides Dr. Shubin, the principal discoverers were Edward B. Daeschler of the Academy of Natural Sciences in Philadelphia and Farish A. Jenkins Jr., a Harvard evolutionary biologist. Casts of the fossils will be on view at the Science Museum of London.
Michael J. Novacek, a paleontologist at the American Museum of Natural History in Manhattan, who was not involved in the research, said: "Based on what we already know, we have a very strong reason to think tetrapods evolved from lineages of fishes. This may be a critical phase in that transition that we haven't had before. A good fossil cuts through a lot of scientific argument."
Dr. Shubin's team played down the fossil's significance in the raging debate over Darwinian theory, which is opposed mainly by some conservative Christians in this country, but other scientists were not so reticent. They said this should undercut the argument that there is no evidence in the fossil record of one kind of creature becoming another kind.
One creationist site on the Web (emporium.turnpike.net/C/cs /evid1.htm) declares that "there are no transitional forms," adding: "For example, not a single fossil with part fins, part feet has been found. And this is true between every major plant and animal kind."
Dr. Novacek responded: "We've got Archaeopteryx, an early whale that lived on land, and now this animal showing the transition from fish to tetrapod. What more do we need from the fossil record to show that the creationists are flatly wrong?"
Duane T. Gish, a retired official of the Institute for Creation Research in San Diego, said, "This alleged transitional fish will have to be evaluated carefully." But he added that he still found evolution "questionable because paleontologists have yet to discover any transitional fossils between complex invertebrates and fish, and this destroys the whole evolutionary story."
Dr. Shubin and Dr. Daeschler began their search on Ellesmere Island in 1999. They were attracted by a map in a geology textbook showing an abundance of Devonian rocks exposed and relatively easy to explore. At that time, the land had a warm climate: it was part of a supercontinent straddling the Equator.
It was not until July 2004, Dr. Shubin said, that "we hit the jackpot." They found several of the fishes in a quarry, their skeletons largely intact and in three dimensions. The large skull had the sharp teeth of a predator. It was attached to a neck, which allowed the fish the unfishlike ability to swivel its head.
If the animal spent any time out of water, said Dr. Jenkins, of Harvard, it needed a true neck that allowed the head to move independently on the body.
Embedded in the pectoral fins were bones that compare to the upper arm, forearm and primitive parts of the hand of land-living animals. The joints of the fins appeared to be capable of functioning for movement on land, a case of a fish improvising with its evolved anatomy. In all likelihood, the scientists said, Tiktaalik flexed its proto-limbs mainly on the floor of streams and might have pulled itself up on the shore for brief stretches.
In their report, the scientists concluded that Tiktaalik was an intermediate between the fishes Eusthenopteron and Panderichthys, which lived 385 million years ago, and early tetrapods. The known early tetrapods are Acanthostega and Ichthyostega, about 365 million years ago.
Tiktaalik, Dr. Shubin said, is "both fish and tetrapod, which we sometimes call a fishapod."
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